The invention relates to a SQUID arrangement for measuring a change in the magnetic field having a direct current SQUID, the change in the magnetic field being caused by a specimen that is arranged in a magnetization field. Moreover, the invention relates to a method for measuring such a change. Finally, the method relates to the use of such a SQUID arrangement or such a method for various applications.
If the change in the magnetization of a specimen is to be measured, this specimen must be disposed for this purpose in a constant magnetic field, the so-called exciter field or magnetization field. A change in the magnetization of the specimen can then be detected as a change in the magnetic field. A superconducting quantum interference detector (SQUID) can measure such a change in the magnetic field in the surroundings of the specimen. The SQUID is coupled to the specimen via a flux transformer. However, the flux transformer transfers only a portion of the magnetic flux and thus also only a portion of the signal energy to the SQUID. Or, in particular in the case of very small specimens, there is direct coupling in that the specimen is placed directly in the SQUID loop. This can reduce a loss in magnetic flux. Such an arrangement is known for instance in U.S. Pat. No. 4,588,947. In both cases, the magnetization field is produced by a separate superconducting coil into which a so-called exciter current or magnetizing current is injected.
One object of the present invention is to provide a simple design in which the losses in the magnetic flux are also simultaneously minimized.